The present invention relates to a device for the presentation of information in vehicle applications, in particular automotive applications.
As is known, a vehicle comprises many devices for the presentation of information to the driver and/or to the passengers; the number and the information content of said devices has increased constantly over the years on account of the increasing information content coming from vehicle systems.
Displays for vehicle applications are generally classified in the following categories:                displays arranged on the dashboard or instrument panel, in front of the driver; these comprise:                    backlit icons for signalling information regarding the state of the vehicle (for example: hand brake, direction indicators, headlights, diagnostics on front and rear lights, foglights, rear foglights, engine-oil temperature, parking brake);            analogical dials for indication of the fuel level, engine r.p.m., vehicle speed, time, etc.;            backlit liquid-crystal displays, for alphanumeric information (total kilometers, partial kilometers travelled, etc.);            backlit liquid-crystal displays of the dot-matrix type, for returning information coming from the body computer (for example, average speed, average and instantaneous consumption, autonomy, etc.);                        displays arranged at the centre of the dashboard, in the area half way between the driver and the passenger; these typically comprise:                    backlit liquid-crystal displays of the active-matrix type, for displaying information coming from the GPS navigator (medium-high range), including indications and maps; the same display is typically used to present additional information (air-conditioning system, radio/CD, telephone, info-telematics, cruise information coming from the body computer, etc.);            alternatively to the foregoing, backlit liquid-crystal displays of the passive-matrix type, for displaying information coming from the GPS navigator (medium-low range), with the exclusion of maps;                        displays arranged on the windscreen or on a viewer set between the driver and the windscreen; these displays are known by the term head-up displays (or HUDs) and afford the possibility of returning information in the following mode:                    superimposed on the background, in the periphery of the field of view of the driver, whilst he performs the primary task of driving; this reduces the movement of eyes/head necessary for the driver to have access to the visual information and hence the time for which the driver takes his eyes off the road;            at a certain distance from the driver, typically ranging from 2 m to infinity, in such a way that the driver does not have to adapt the focal length of his eye for accessing the information.                        
HUDs are typically used for returning information regarding navigation, or information that is critical for the safety of the vehicle; they can also be used for night vision.
Notwithstanding the possible ergonomic advantages deriving from the use of displays of a HUD type, their diffusion is currently limited by the following factors:
i. cost of the system;
ii. difficulty of installation/alignment;
iii. encumbrance of the projection-optics chain, which is typically installed in the dashboard between the visor or sun-shield of the instrument panel and the windscreen;
iv. high consumption of the source of light in so far as the light that reaches the driver's eye is only a minimal fraction of the light emitted by the projection-optics chain (the luminance of the image is equal to 10-20% of the luminance at output from the projection-optics chain); this is rendered necessary by the fact that the reflecting screen, whether the windscreen or a viewer set between the windscreen and the driver, must transmit at least 80% of the light coming from the road so as not to obstruct vision;
v. reduced angle of visibility, in the sense that a movement of the driver's head greater than a certain amount (defined by the so-called head-motion-box or HMB) could lead the information either totally or partially to exit from the driver's field of view.
In HUD systems according to the known art (an example of which is represented in FIG. 1), the solution of one or more of these problems entails a complication of the others; purely by way of example, the enlargement of the HMB, referred to in point v, entails the use of projection optics of larger diameter, with a consequent increase in costs, referred to in point i, and in encumbrance, referred to in point iii.
With reference to FIG. 1, the light emitted by an image source 100 (for example, a microdisplay) is captured by a projection optics (Schmidt system), made up of a first mirror 101 and a second mirror 102, and is projected onto the windscreen 40 through a transparent protective window 103 typically positioned on the vehicle dashboard.
The mirror 102 is typically a complex aspherical mirror, the function of which is that of generating a virtual image of the source 100 (in combination with the first mirror 101) and of compensating the distortions of the image deriving from the asphericity of the windscreen 40.
The windscreen 40 reflects a percentage of the light coming from the projection optics towards the driver's eyes. In this way, the driver perceives a virtual image 60, which is located at a certain distance from the windscreen, said distance depending upon the projection optics, and is superimposed on the background 70.